A smartphone camera can make you a walking gamma ray detector. Without needing any extra hardware, you could get a warning on your phone when you're approaching potentially harmful levels of gamma radiation.

Scientists at Idaho National Laboratory created an Android app (the system is called CellRAD) for turning smartphone cameras into radiation detectors, and tested it with four smartphone models (Samsung Nexus S, Samsung Galaxy Nexus, Samsung SIII and LG Nexus 4).

They concluded that the phones have the processing power to detect gamma radiation with their built-in cameras and to measure levels on the phone. With the help of a program on a remote server, the app captures and measures an average energy level, then uses a model to figure out what types of radioactive material could be emitting the radiation. Basically, once your phone has been calibrated with the app, you'll have a radiation detector in your pocket.

"Up until fairly recently, people weren't carrying around cameras with computers attached to them pretty much all the time," says Joshua Cogliati, a research scientist and co-author of the recent paper announcing their findings. "That's why it's happening now."

The app was funded by a grant from the Department of Defense's Rapid Reaction Technology Office and could be useful for firefighters, police officers and other first responders, according to its creator.

The principle behind this isn't new — scientists know that charge-coupled devices (or CCDs used in cameras) can detect X-rays. But now our phones have the computing power to figure out what the source of radiation is, and eliminate false positives that can happen just because your phone is warm.

The U.S. Nuclear Regulatory Commission says members of the public shouldn't be exposed to more than 0.1 rem of radiation a year; Cogliati says the app will be able to quickly pick up a source before a person receives a dose of that amount, and it's not so sensitive that it'll start beeping at bananas. Of course it won't be as sensitive as a regular detector, but it's definitely enough to detect radiation before it reaches deadly levels and it's useful enough as a warning system, he says.

For example, say you know there's a large radioactive source somewhere in New York City.

"New York has people who do have radiation detectors, but they're not able to go quite everywhere," Cogliati says. "All of a sudden you might be able to push [radiation detectors] to all the police officers who have cell phones and suddenly you've just increased your coverage."

The scientists are considering a commercial partnership to develop the app for the general public. In the meantime, there are otherapps that can give you an estimate of the gamma radiation around you.